But to address some of those concerns.
While errors in the config can cause big problems, it's not very common for people to change it once it's installed. It's like doing changes to the kernel, Apache, or Xorg settings. Sure, things can easily be broken there but for the common case, the defaults are good once one has passed the installation wizard/guide.
In case of SSL issues between mail servers, I am rather sure that postfix only does a best-effort. Thus if your certification expires, they will fall back to plain text. However most CA's will warn you several times once it gets close to the one year mark, so it's not a very big workload to handle. If you know of an email server that will cancel delivery, please let me know as I would be very interested to hear it.
PTR is a real issue, but if you have static IP, PTR records should be rather easy to get. It is also a one time cost for the domain name. For a company network, a static IP and support is commonly included in the price. You email/call them, and they add a PTR. For private users, a VPN solution might be needed in some cases, but I'm unsure if it's that much of an requirement. Gmail seems fine in sending emails to locations without PTR, or receiving emails from servers without one. However I have not tested this fully or with other services like to Apple or Microsoft.